It is known that the Profinet IO is the Ethernet-based automation standard from the Profibus user organization (PNO) and is essentially 100% based on the Ethernet standard (according to IEEE 802.3), operates in full duplex mode and supports switched Ethernet at a transmission rate of 100 Mb/s. This means that process and production data are available not just at the field level but rather can seamlessly enter multiregional data acquisition systems, so that it also becomes possible to integrate local peripheral areas in a vertical direction.
In contrast to Profibus, which operates on the basis of the “master-slave model”, Profinet IO operates essentially on the basis of the producer-consumer model. This saves call telegrams, inter alia, and means that an entire group of “consumers”, that is to say the network subscribers connected in the Profinet IO network, such as I/O components and field transmitters, is reached simultaneously with one telegram, so that this allows very efficient homogeneous integration of the world of automation into the IT environment. In addition, besides the known, tried and tested Profibus standards the integration of other field bus concepts within the Profinet IO concept is also ensured.
One fundamental difference between Profibus and Profinet IO applications is the different addressing of the devices of the network subscribers incoporated or to be incorporated in a respective network.
In contrast to the Profibus, the respectively incorporated network subscribers within a Profinet IO network are addressed using each subscriber device's own distinct MAC address and also a logical IP address which is distinctly associated with this physical address. IP addresses are conventionally allocated using DHCP (Dynamic Host Configuration Protocol), a mechanism comparable therewith or using the Profinet-IO-specific protocol DCP (Discovery Configuration Protocol). Specifications recommend the use of DHCP in large installations and of DCP in small installations.
Before the physical and logical network addresses are associated, however, each Profinet IO network subscriber needs to be allocated a symbolic name for identification in the network for the purpose of subsequent distinct addressing. This symbolic name, subsequently called station identifier, must usually be of DNS (Domain Name Service) compliant structure and is set on the network subscriber before said subscriber can be operated in a Profinet IO system. This allocation is frequently also called “baptism”.
In this context, the station identifier is allocated manually using a software tool, with the station identifier to be allocated and the subscriber being associated by means of the distinct Ethernet MAC address. The setting is then made by the user using a software tool with the aid of a network-subscriber-specific engineering tool or using the network by supporting defined DCP services.
When the station identifier is allocated, the user therefore needs to know the respective MAC address.
Whether a network subscriber subsequently receives its IP address from the IO controller or obtains it or reads it from a DHCP server can also be stipulated within this context.
If the IO controller allocates IP addresses, the IO controller loads a nominal configuration for IO network subscriber devices from its engineering system, the station identifier being prescribed for each IO network subscriber device.
Using a special DCP service (Identify), multicasting is then used to look for the network subscriber which belongs to a particular station identifier. In the response, this network subscriber returns its own MAC address. A DCP service (Set-IP) is then used by the IO controller to assign each IO network subscriber its nominal IP address. Following this association, the network subscriber needs to initialize its TCP/IP stack with this address. When the IP address has been set successfully, a communication link is set up to the IO network subscriber.
In this context, the nominal IP address may already be held in the nominal configuration or is read from a DNS server by the IO controller.
With regard to the allocation of the station identifier on the basis of the prior art, further fundamental drawbacks arise particularly when a network subscriber is interchanged, since an interchanged device in the Profinet IO system must first of all be provided with the original station identifier again.
In the case of repair, this is frequently possible only with special knowledge, particularly when a complex software tool needs to be used.
If the station identifier is filed in the device on a removable storage medium, which is easily interchanged in principle, however, this results in increased costs. In addition, there is the increased opportunity for theft, particularly if standard media which are in circulation, such as Compact Flash memory cards, are used.
In addition, the manual operation of allocating station identifiers is susceptible to error and is a complex process overall.
There is, therefore, a need to demonstrate a way of ensuring the allocation of station identifiers, which are needed in Profinet IO systems and on the basis of which the subsequent automatic network subscriber device addressing is performed by ascertaining and associating logical and physical addresses, in a much simpler and more error-resistant manner.